1. Field of the Invention
This invention relates to methods, devices and system for recording of electrical signals from neurons.
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3. Description of Related Art
Understanding how the brain functions by recording the electrical activity of brain cells (neurons) has been pursued by neuroscientists and clinicians. The underlying mechanism of how neurons fire and interact can be translated into skilled and precise movements, and understanding the mechanism can be used as a tool for diagnosing brain diseases. It has been shown that recorded neuron activities from the motor cortex can be used to control a robotic device [1]-[2]. Neuroscientists have employed neuron recording from scalp or chronically implanted intracranial electrodes to investigate the electrophysiological activity for epileptic seizure detection and prediction [2]. Those experiments involved recording a large population of neurons and thus stimulated the need for the development of a multi-channel neuron recording system.
Challenges of designing a neuron recording system is highly correlated with the characteristics of the physiological neuron signals. The recording device must be able to record these signal with a large dynamic range in terms of signal amplitude and frequency, and to reject the DC offset occurring at the electrode-electrolyte interface. Power consumption of the system has to be reduced for long-term operation and to avoid elevating the temperature of brain tissue which could cause permanent damages [3]. The electrode impedance and amplifier input impedance form a voltage divider and thus the practical neuron signal shown at amplifier input is smaller than its actual value.
The degradation is severe for local field potentials (LFPs) recording because electrode impedance is much higher at 10 Hz than its value at 1-kHz [4]. If the neural signal at the recording amplifier input is seriously attenuated, it is difficult to be differentiated from the background noise. In addition, the next generation of this recording system should have the capability to process an enormous amount of neural information via signal detection, feature extraction, pattern classification and other mechanisms. A future recording system should also have the capability of reducing the amount of data to be transmitted and/or extracting a stable control signal from a large neuron pool in order to control prosthetic devices. The design challenges noted above can be translated into low-voltage and low-power design necessitating an advanced technology node. The present invention addresses at least some of these challenges.